JPH0765215B2 - Zn-based alloy-plated steel sheet excellent in chipping resistance and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention relates to a Zn-based alloy-plated steel sheet used for automobile bodies, outer surface materials, and the like, and particularly a Zn-based alloy-plated steel sheet having excellent chipping resistance and a method for producing the same. Regarding

<Prior Art and Its Problems> In recent years, in order to prevent corrosion of automobile bodies, high corrosion resistance of automobile steel sheets has been demanded, and development thereof has been advanced. The cause of deterioration of corrosion resistance is poor chemical conversion treatment of Zn alloy plating, which results in poor secondary water adhesion after 3 coats, and pebbles on the road bounce off the exterior surface of automobiles. There is peeling of the plating film due to chipping (chipping property).

With respect to the problem of poor water-resistant secondary adhesion, the chemical conversion treatment liquid has been improved, and at present it is at a level where there is almost no problem.

Regarding chipping resistance, plating of 1 to 1000 mg / m ² consisting of one or more of Cr, Mn, Fe, Ni, Zn, etc. (hereinafter referred to as substrate adjustment plating), and then Zn-based alloy plating or composite A method of forming electroplating (hereinafter referred to as the main plating layer) (Japanese Patent Laid-Open No. 59-200789), or electroplating a Zn-Ni alloy having a Ni content higher than that of the main plating layer to a thickness of 0.05 to 0.8 μm ( Zn-Ni after pre-plating)
Those to be plated (Japanese Patent Publication No. 61-439) are considered.

However, in the above method, it is necessary to separately provide equipment for substrate conditioning plating or pre-plating, and a large amount of equipment cost is required. Moreover, since an electrolytic solution different from the main plating solution is required, the management of the plating solution becomes complicated, which is economically disadvantageous.

<Purpose of the Invention> The present invention is intended to solve the above-mentioned drawbacks of the prior art, and is to provide a Zn-based alloy-plated steel sheet excellent in corrosion resistance, particularly chipping resistance, and a manufacturing method thereof.

<Structure of the Invention> The chipping resistance is the adhesion between the steel plate and the plating layer against the stress received by hitting the steel plate with flying stones. Since the Zn-based alloy-plated steel sheet is hard and lacks in ductility, the stress received is rarely absorbed by the elongation of the plating or the like and is directly transmitted to the plating-cold-rolled steel sheet interface.

On the other hand, in Zn-based alloy plating, the stress inherent in the plating layer itself due to crystal distortion due to alloying increases, and the bond strength between the plating and cold-rolled steel sheet is small.

From this, it is considered that the chipping resistance can be improved by dispersing the stress received at points or by increasing the bonding force between the plated and cold rolled steel sheets.

As a result of diligent research on a method for dispersing stress received by the present inventors, the present invention provides a depression of a certain pattern on the surface of a cold-rolled steel sheet and performs plating, and the Zn-based alloy-plated steel sheet is received at the point. It has been discovered that stress is efficiently dispersed and chipping resistance is improved.

That is, the first embodiment of the present invention is temper-rolled by laser processing using a work roll having a specific surface pattern, and the center line average roughness Ra of the surface is 0.3 to 2.0 μm and Rmax.
Is in the range of 6 to 25 μm, and has a Zn-based alloy plating film on a cold-rolled steel sheet in which at least one concave portion having a depth of 6 μm or more is present while being surrounded by a square having an arbitrary side of 800 μm. It is a Zn-based alloy plated steel sheet.

According to a second aspect of the present invention, a surface of a work roll for temper rolling is subjected to a patterning process for forming a surface pattern of convex portions and concave portions using a laser, and the work roll having the surface pattern is prepared. By temper rolling on one or both sides of the steel sheet to be temper rolled with temper rolling elongation λ of 0.3% or more, the center line average roughness Ra of the surface is in the range of 0.3 to 2.0 μm and Rmax in the range of 6 to 25 μm. Yes, transfer the pattern of the work roll surface to the steel plate surface so that at least one recess with a depth of 6 μm or more is surrounded by a square of 800 μm on any side, and then apply Zn alloy plating. Is a method for producing a Zn-based alloy-plated steel sheet having excellent chipping resistance.

Further, the Zn-based alloy plating is preferably electroplating, and the electroplating may be carried out by a small amount of plating in advance, followed by immersion in a plating bath for 40 seconds and then electroplating.

Next, the Zn-based alloy plated steel sheet of the present invention will be described in detail.

In the present invention, chipping is such that impact is dispersed, so that the surface roughness of the steel sheet used is preferably in the range described below.

The center line average roughness Ra of the surface is preferably in the range of 0.3 to 2.0 μm. The reason for this is that if the thickness is less than 0.3 μm, the holding power of oil will decrease and cracking will occur during press working.
This is because if it exceeds 0 μm, the image clarity after coating is deteriorated.

Rmax is preferably in the range of 6 to 25 μm. This is because if the thickness is less than 6 μm, the chipping property cannot be sufficiently improved.
This is because if it exceeds m, the sharpness after coating is deteriorated.

The center line average roughness of the steel sheet surface means that the center line is the X axis,
It is defined by the following formula with the vertical direction as the Y axis.

Rmax is the maximum height from the center line at a measured length of 2.5 mm.

FIG. 1 is an experimental result showing the influence of the depth of the recess and the distance between the recesses on the chipping resistance, which was carried out in the same manner as in Examples and Comparative Examples described later. As the chipping resistance test, a gravure test was performed. Gravelo test is that 20 g of 1 g / granite is dropped into a cylinder of 50 mmφ and hammered onto a Zn-based alloy-plated steel sheet cooled to −15 ° C. with an air pressure of 4 kg / cm ² introduced into the cylinder. For the evaluation, 5 points having a large peeling diameter are actually measured and judged according to the following criteria.

○ Average value 4 mm or less Max 5 mm or less △ Average value 4 mm or less Max 5 mm or more × Average value 4 mm or more From Fig. 1, when the depth of the depressions is 6 μm or more and the distance between the depressions is 800 μm or less, good chipping resistance Is. If the recess depth is less than 6 μm, the chipping resistance is poor regardless of the distance between the recesses. Distance between depressions is 800
If the depth is more than μm, the chipping resistance gradually deteriorates even if the recess depth is 6 μm or more, and the characteristics deteriorate.

The reason why these phenomena occur is that the depressions on the surface of the cold-rolled steel sheet have the effect of dispersing the stress received at the points from the stepping stones. In order to disperse the stress, it is considered necessary that the size of the flying stone, a certain depth or more of the depression depth and a certain depth or more of the depression density depending on the magnitude of the stress exist.

Zn-based alloy plating described in the present invention is Zn-Ni,
Binary alloy plating such as Zn-Fe, Zn-Mn, and Zn-Al, and ternary alloy plating such as Zn-Ni-Co and Zn-Fe-Co are shown. It is not limited to electroplating.

Next, the method for producing the Zn-based alloy plated steel sheet of the present invention will be described in detail.

The work roll used in the present invention has a convex portion and a concave portion formed on the surface thereof by a high-density laser energy source. The pattern may be any pattern as long as it can impart the above surface shape to the surface of the steel sheet. Temper rolling is performed on one side (or both sides) of a steel sheet with a temper rolling elongation λ of 0.3% or more. This is because when λ is less than 0.3%, elongation at yield does not disappear and stretcher strain occurs during press working.

The above-mentioned Zn-based alloy plating, for example, electroplating is performed on the cold-rolled steel sheet that has been temper-rolled as described above.

Shot blasting, electric discharge machining, and the like are used as the high-density energy source for forming the surface pattern of the convex and concave portions on the surface of the temper rolling work roll, but a laser is used. This is because the surface pattern can be easily controlled.

For the Zn-based alloy electroplating, what is called a trace amount plating-immersion plating method (Japanese Patent Publication No. 61-148888) is preferable.

The micro-plating-immersion plating method is a method in which a micro-plating of 100 to 3000 mg / m ² is first carried out, and then a normal electroplating is carried out after being immersed in a plating bath for 40 seconds or less. If the immersion time is longer than 40 seconds, productivity will be reduced and it is uneconomical. The Zn-based alloy-plated steel sheet obtained by this method can remarkably improve the chipping resistance at low temperatures.

The reason for this is not clear, but during immersion plating, minute cracks are generated in the trace amount plating layer, and the stress at the plating layer-material interface is released, thereby improving the adhesion at the plating layer-material interface. .

<Example> The present invention will be specifically described below with reference to Examples and Comparative Examples.

(Example-1) Using a work roll for temper rolling in which an uneven shape pattern was formed on the surface using a laser, temper tempering was applied to one side of a 0.7 mm-thick SPCE cold-rolled steel sheet at a temper rolling elongation rate of 0.5%. By rolling, a cold-rolled steel sheet with recesses whose Ra, Rmax, recess depth, and distance between recesses are shown in Table 1 was obtained.

An example of the cross-sectional pattern of the cold rolled steel sheet is shown in Fig. 2a, Fig. 2b or Fig. 2c.

FIG. 2 was measured with a stylus roughness meter (manufactured by Tokyo Seimitsu Co., Ltd.).

The cold rolled steel sheet was plated with Zn-Ni or Zn-Fe. The Zn-Ni plating conditions were: ZnSO ₄ 7H ₂ O 120g / NiSO ₄ 6H ₂ O 250g / Na ₂ SO ₄ 50g / pH2, bath temperature 50 ° C, current density 100A / dm ² , 3
It was plated with 0 g / m ² .

The Zn-Fe plating conditions were: ZnSO ₄ 7H ₂ O 200g / FeSO ₄ 7H ₂ O 250g / Na ₂ SO ₄ 50g /, pH 1.5, hot liquid 50 ° C, current density 100A / d.
It was plated with m ² and 30 g / m ² .

After Zn-Ni plating or Zn-Fe plating, three coats of dipping-type phosphate chemical conversion treatment, a cationic electrodeposition coating, an intermediate coat and a top coat, which are usually commercially available, were applied in a total thickness of 90 μm. The chipping resistance was evaluated by the gravure test described above, and the results shown in FIG. 1 and Table 1 were obtained.

(Example-2) After the same cold-rolled steel sheet as in Example-1 was microplated under the same conditions as in Example-1, immersion plating was performed in the same bath as in Example-1. Table 2 shows the plating type, the amount of plating, and the plating time at the time of immersion plating at the time of minute amount plating.

Then, 30 g / m ² of electroplating was performed in the same bath at a current density of 100 A / dm ² .

Evaluation of chipping resistance is performed in the gravure test described above,
The results shown in Table 2 were obtained.

(Comparative Example-1) Using a work roll for temper rolling with concave and convex surface patterns using a laser, temper rolling on one side at a temper rolling elongation of 0.5%, Ra, A cold rolled steel sheet was obtained in which Rmax, the depth of the depressions, and the distance between the depressions were as shown in Table 3. The same plating treatment as in Example 1 was performed to obtain a Zn-based alloy plated steel sheet. The chipping resistance was evaluated by the gravure test described above. The results shown in FIG. 1 and Table 3 were obtained.

<Effects of the Invention> As described above, the present invention is a Zn-based alloy-plated steel sheet obtained by subjecting a cold-rolled steel sheet having an appropriate surface roughness pit depth and distribution to Zn-based alloy plating, preferably electroplating. Therefore, the chipping resistance can be improved.

In the production method of the present invention, the initial cost of equipment is reduced, complicated bath control is not required, and workability is efficient.

By using a laser as a high-density energy source, work rolls can be adjusted easily and quickly. .

By using the trace amount plating-immersion plating method for the Zn-based alloy electroplating, the chipping resistance at low temperatures can be further improved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing an appropriate range of chipping resistance according to a surface pattern of a cold rolled steel sheet. FIG. 2a, FIG. 2b and FIG. 2c are views showing the sectional pattern of the cold-rolled steel sheet with depressions.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A 61-67794 (JP, A) JP-A 57-165000 (JP, A) JP-A 54-150331 (JP, A) JP-A 59- 48190 (JP, A) JP 59-89787 (JP, A) JP 59-85883 (JP, A) JP 58-193389 (JP, A) JP 59-104201 (JP, A)

Claims (3)

[Claims] 1. Laser tempering is heat-rolled using a work roll having a specific surface pattern, and the surface has a center line average roughness Ra of 0.3 to 2.0 μm and Rmax of 6 to 25 μm. Zn-based alloy with excellent chipping resistance, characterized in that it has a Zn-based alloy plating film on a cold-rolled steel sheet in which at least one recess with a depth of 6 μm or more is present while being surrounded by a square of 800 μm on each side. Plated steel sheet. 2. A surface of a work roll for temper rolling is subjected to a patterning process for forming a surface pattern of protrusions and depressions by using a laser, and the work roll having the surface patterned should be temper rolled. By temper-rolling one or both sides of the steel sheet with temper rolling elongation λ of 0.3% or more, the center line average roughness Ra of the surface is 0.3 to 2.0 μm and Rmax is 6 to 25 μm.
The area of the work roll surface is surrounded by a square of 800 μm, and the work roll surface pattern is transferred to the steel plate surface so that there are at least one recess with a depth of 6 μm or more. A method for producing a Zn-based alloy-plated steel sheet having excellent chipping resistance, which is characterized by carrying out. 3. The Zn-based alloy plating is electroplating,
The electroplating is a method of performing a small amount of plating in advance, and subsequently, immersing it in a plating bath for 40 seconds or less, and then performing electroplating, which is excellent in chipping resistance according to claim 2. Method for manufacturing alloy-plated steel sheet.